If you’re like most of us, you’re not even sure there’s a difference between the two terms. There is.
A synopsis goes much further. It highlights all the plot points – and sub-plot points – and takes you through the entire story. It usually leaves out character development almost completely, as well as all the other things that make the story interesting. But it does include all the plot twists and surprises.
So, a summary gives you enough to whet your appetite so you will then go and read the book or article. A synopsis pretty much ruins it if you then go and read the book or article.